1. Field of the Technology
This invention relates generally to magnetic sensing devices, and more particularly to the use of a plurality of oxidized, nitrided, or oxynitrided insulator structures, such as capping layer structures, in magnetic sensing devices.
2. Description of the Related Art
Computers often include auxiliary memory storage devices having media on which data can be written and from which data can be read for later use. A direct access storage device (disk drive) incorporating rotating magnetic disks are commonly used for storing data in magnetic form on the disk surfaces. Data is recorded on concentric, radially spaced tracks on the disk surfaces. Magnetic heads including read sensors are then used to read data from the tracks on the disk surfaces.
In high capacity disk drives, magnetoresistive read (MR) sensors, commonly referred to as MR heads, are the prevailing read sensors because of their capability to read data from a surface of a disk at greater linear densities than thin film inductive heads. An MR sensor detects a magnetic field through the change in the resistance of its MR sensing layer (also referred to as an “MR element”) as a function of the strength and direction of the magnetic flux being sensed by the MR layer.
The conventional MR sensor operates on the basis of the anisotropic magnetoresistive (AMR) effect in which the MR element resistance varies as the square of the cosine of the angle between the magnetization of the MR element and the direction of sense current flow through the MR element. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium (the signal field) causes a change in the direction of magnetization in the MR element, which in turn causes a change in resistance in the MR element and a corresponding change in the sensed current or voltage.
Another type of MR sensor is the giant magnetoresistance (GMR) sensor manifesting the GMR effect. In GMR sensors, the resistance of the MR sensing layer varies as a function of the spin-dependent transmission of the conduction electrons between magnetic layers separated by a non-magnetic layer (spacer) and the accompanying spin-dependent scattering which takes place at the interface of the magnetic and non-magnetic layers and within the magnetic layers. GMR sensors using only two layers of ferromagnetic material (e.g., nickel-iron, cobalt-iron, or nickel-iron-cobalt) separated by a layer of nonmagnetic material (e.g., copper) are generally referred to as spin valve (SV) sensors manifesting the SV effect. In an SV sensor, one of the ferromagnetic layers, referred to as the pinned layer, has its magnetization typically pinned by exchange coupling with an antiferromagnetic (AFM) layer (e.g., iridium-manganese, iridium-manganese-chromium, or platinum-manganese) layer. The pinning field generated by the AFM layer should be greater than demagnetizing fields to ensure that the magnetization direction of the pinned layer remains fixed during application of external fields (e.g. fields from bits recorded on the disk). The magnetization of the other ferromagnetic layer, referred to as the sensing layer, however, is not fixed and is free to rotate in response to the field from the information recorded on the magnetic medium (the signal field). A cap or capping layer of tantalum is typically formed over the sensor stack structure for protecting the sensor during and after its production.
Tunneling magnetoresistance (TMR) sensors have a configuration similar to GMR sensors, except that the magnetic layers of the sensor are separated by an insulating film thin enough to allow electron tunneling between the magnetic layers. The tunneling probability of an electron incident on the barrier from one magnetic layer depends on the character of the electron wave function and the spin of the electron relative to the magnetization direction in the other magnetic layer. As a consequence, the resistance of the TMR sensor depends on the relative orientations of the magnetization of the magnetic layers, exhibiting a minimum for a configuration in which the magnetizations of the magnetic layers are parallel and a maximum for a configuration in which the magnetizations of the magnetic layers are anti-parallel.
Another type of non-volatile magnetic device is a GMR and/or TMR based magnetic memory cell. An array of magnetic memory cells is often called magnetic random access memory (MRAM). The magnetic memory cell may include a sensing layer and a reference layer that is separated from the data layer by a tunnel barrier layer. These memory cells make use of GMR and TMR within the multi-layer structure. In a magnetic memory cell, a bit of data may be stored by “writing” into the data layer via one or more conducting leads (e.g., a bit line and a word line). The write operation is typically accomplished via a write current that sets the orientation of the magnetic moment in the sensing layer to a predetermined direction. Once written, the stored bit of data may be read by providing a read current through one or more conducting leads (e.g., a read line) to the reference layer. In at least one type of magnetic memory cell, the read current sets the orientation of the magnetic moment of the reference layer in a predetermined direction. For each memory cell, the orientations of the magnetic moments of the sensing layer and the reference layer are either parallel (in the same direction) or anti-parallel (in different directions) to each other giving rise to four different magnetic states. The degree of parallelism affects the resistance of the cell, and this resistance can be determined by sensing (e.g., via a sense amplifier) an output current produced by the memory cell in response to the read current through a GMR or TMR measurement.
There are several properties of magnetic sensing device which, if improved, will improve the performance and increase storage capacity. For example, it is generally desirable to increase the magnetoresistive effect (ΔR/R) and decrease the coercivity (Hce) of the sensing layer without substantially increasing the thickness of the sensor layers. An increase in the magnetoresistive effect equates to higher bit density (bits/square-inch of the rotating magnetic disk). The capping layer structure of an SV sensor, as well as the tunnel barrier layer of a TMR sensor has an effect on these sensor properties.
Referring now to the drawings wherein like reference numerals designate like or similar parts throughout the several views, FIGS. 1-3 illustrate a magnetic disk drive 30. Disk drive 30 includes a spindle 32 that supports and rotates a magnetic disk 34. Spindle 32 is rotated by a spindle motor 36 that is controlled by a motor controller 38. A slider 42 includes a combined read and write magnetic head 40 and is supported by a suspension 44 and actuator arm 46 that is rotatably positioned by an actuator 47. A plurality of disks, sliders, and suspensions may be employed in a large capacity direct access storage device (DASD) as shown in FIG. 3. Suspension 44 and actuator arm 46 are moved by actuator 47 to position slider 42 so that magnetic head 40 is in a transducing relationship with a surface of magnetic disk 34. When disk 34 is rotated by spindle motor 36, slider 42 is supported on a thin (typically, 0.05 μm) cushion of air (air bearing) between the surface of disk 34 and an air bearing surface (ABS) 48. Magnetic head 40 may then be employed for writing information to multiple circular tracks on the surface of disk 34, as well as for reading information there from. Processing circuitry 50 exchanges signals, representing such information, with head 40, provides spindle motor drive signals for rotating magnetic disk 34, and provides control signals to actuator 47 for moving slider 42 to various tracks. In FIG. 4, slider 42 is shown mounted to a suspension 44. The components described hereinabove may be mounted on a frame 54 of a housing 55, as shown in FIG. 3. FIG. 5 is an ABS view of slider 42 and magnetic head 40. Slider 42 has a center rail 56 that supports magnetic head 40, and side rails 58 and 60. Rails 56, 58 and 60 extend from a cross rail 62. With respect to rotation of magnetic disk 34, cross rail 62 is at a leading edge 64 of slider 42 and magnetic head 40 is at a trailing edge 66 of slider 42.
FIG. 6 is a side cross-sectional elevation view of a merged magnetic head 40, which includes a write head portion 70 and a read head portion 72. Read head portion 72 includes a giant magnetoresistance (GMR) read head which utilizes a spin valve (SV) sensor 74 of the present invention. FIG. 7 is an ABS view of FIG. 6. SV sensor 74 is sandwiched between nonmagnetic electrically insulative first and second read gap layers 76 and 78, and read gap layers 76 and 78 are sandwiched between ferromagnetic first and second shield layers 80 and 82. In response to external magnetic fields, the resistance of SV sensor 74 changes. A sense current Is conducted through the sensor causes these resistance changes to be manifested as potential changes. These potential changes are then processed as read back signals by processing circuitry 50 shown in FIG. 3.
Write head portion 70 of magnetic head 40 includes a coil layer 84 sandwiched between first and second insulation layers 86 and 88. A third insulation layer 90 may be employed for planarizing the head to eliminate ripples in the second insulation layer caused by coil layer 84. The first, second and third insulation layers are referred to in the art as an “insulation stack”. Coil layer 84 and first, second and third insulation layers 86, 88 and 90 are sandwiched between first and second pole piece layers 92 and 94. First and second pole piece layers 92 and 94 are magnetically coupled at a back gap 96 and have first and second pole tips 98 and 100 which are separated by a write gap layer 102 at the ABS. Since second shield layer 82 and first pole piece layer 92 are a common layer, this head is known as a merged head. In a piggyback head an insulation layer is located between a second shield layer and a first pole piece layer. As shown in FIGS. 2 and 4, first and second solder connections 104 and 106 connect leads from SV sensor 74 to leads 112 and 114 on suspension 44, and third and fourth solder connections 116 and 118 connect leads 120 and 122 from the coil 84 (see FIG. 8) to leads 124 and 126 on suspension 44.
FIG. 9 is an enlarged isometric ABS illustration of read head 40 shown in FIG. 7 which includes SV sensor 74. First and second hard bias and lead layers 134 and 136 are connected to first and second side edges 138 and 139 of SV sensor 74. This connection is known in the art as a contiguous junction and is fully described in commonly assigned U.S. Pat. No. 5,018,037 which is incorporated by reference herein. First hard bias and lead layers 134 include a first hard bias layer 140 and a first lead layer 142, and second hard bias and lead layers 136 include a second hard bias layer 144 and a second lead layer 146. Hard bias layers 140 and 144 cause magnetic fields to extend longitudinally through SV sensor 74 for stabilizing the magnetic domains therein. SV sensor 74 and first and second hard bias and lead layers 134 and 136 are located between the nonmagnetic electrically insulative first and second read gap layers 76 and 78. First and second read gap layers 76 and 78 are, in turn, located between ferromagnetic first and second shield layers 80 and 82.
FIG. 10 shows an ABS illustration of a typical multi-layered structure of a SV sensor 200 located between first and second read gap layers 76 and 78. This read element may be utilized in the slider and disk drive shown and described above in relation to FIGS. 1-8. SV sensor 200 includes a non-magnetic electrically conductive spacer (S) layer 202 which is located between an antiparallel (AP) pinned layer structure 204 and a sensing layer structure 206. AP pinned layer structure 204 includes an antiparallel coupling (APC) layer 208 which is located between first and second ferromagnetic AP pinned layers (AP1) and (AP2) 210 and 212. First AP pinned layer 210 is exchange coupled to an antiferromagnetic (AFM) pinning layer 214 which pins a magnetic moment 215 of first AP pinned layer 210 perpendicular to the ABS in a direction out of or into sensor 200, as shown in FIG. 10. By strong antiparallel coupling between first and second AP pinned layers 210 and 212, a magnetic moment 216 of second AP pinned layer 212 is antiparallel to magnetic moment 215. A seed layer (SL) 222 may be provided between first read gap layer 76 and pinning layer 214 for promoting a desirable texture of the layers deposited thereon. Sensing layer structure 206 includes first and second free ferromagnetic layers (F1) and (F2) 224 and 226, with first sensing layer 224 interfacing spacer layer 202. Sensing layer structure 206 has a magnetic moment 228 which is oriented parallel to the ABS and to the major planes of the layers in a direction from right to left, or from left to right, as shown in FIG. 10. A capping layer structure (C10) 1002 is formed over sensing layer structure 206 for protecting the sensor.
When a signal field from the rotating magnetic disk rotates magnetic moment 228 into the sensor, magnetic moments 228 and 216 become more antiparallel which increases the resistance of the sensor to the sense current (IS). When a signal field rotates magnetic moment 228 of sensing layer structure 206, magnetic moments 228 and 216 become more parallel which reduces the resistance of sensor 200 to the sense current (IS). These resistance changes are processed as playback signals by processing circuitry (i.e. processing circuitry 50 of FIG. 3).
The following materials are examples of materials which may be utilized in multilayered SV sensor 200 of FIG. 10. Seed layer 222 may be made of nickel-iron-chromium (NiFeCr), or alternatively any suitable material; AFM layer 214 may be made of platinum-manganese (PtMn) or alternatively of iridium-manganese (IrMn); AP pinned layers 210 and 212 may be made of cobalt-iron (CoFe); APC layer 208 may be made of ruthenium (Ru); first and second sensing layers 224 and 226 may be made of CoFe, nickel-iron (NiFe), or alternatively any suitable material; spacer layer 202 may be made of copper (Cu); and capping layer structure 1002 is a combination of tantalum (Ta) metal, tantalum oxide (Ta2O5), and diffused oxygen (O). A Cu diffusion barrier layer may be located over and adjacent second sensing layer 226 for effectively increasing conduction electrons back into the mean free path of sensing layer structure 206. Thicknesses of particular materials may be 30 Å of NiFeCr for seed layer 222; 150 Å of PtMn for AFM layer 214, 30 Å of CoFe for first AP pinned layer 210; 4.5 Å of Ru for APC layer 208; 30 Å of CoFe for second AP pinned layer 212; 20 Å of Cu for spacer layer 202; 15 Å of CoFe for first sensing layer 224; 18 Å of NiFe for second sensing layer 226; and 40 Å of a combination of Ta, Ta2O5, and diffused oxygen for capping layer structure 1002.
Conventional methods of making capping layer structure 1002 of FIG. 10 involve the steps of depositing a metallic layer (e.g. between about 20 Å and about 40 Å) in-situ and subsequently exposing that metallic layer to oxygen ex-situ to ambient atmosphere. The depth of oxygen (O) diffusion into the metallic layer is difficult to precisely control. Furthermore, the form in which the diffused oxygen is found (if at all) throughout such layer is of importance to sensor performance.
The oxygen may diffuse only to a certain depth into the metallic layer since the ex-situ oxidation is from the top. Only an upper portion (C103) 1008 of the metallic layer may be sufficiently oxidized from the ex-situ oxidation. In upper portion 1008, the diffused oxygen may be strongly bonded to the Ta in the Ta lattice due to the formation of Ta—O valence bonds, as in the stable compound tantalum oxide (Ta2O5). In a middle portion (C102) 1006 of the metallic layer, the diffused oxygen may be loosely bonded in a lower concentration than that found in upper portion 1008, probably in interstitial sites of the Ta lattice. Non-bonded Ta atoms may also be present in middle portion 1006 of the metallic layer. In a lower portion (C101) 1004 of the metallic layer, diffused oxygen may not be found in any appreciable concentration (i.e. lower portion 1004 may be substantially pure Ta). As in middle portion 1006, non-bonded Ta atoms may be present in lower portion 1004. This non-bonded Ta may diffuse into underlying ferromagnetic materials, such as sensing layer structure 206, and therefore create a magnetic dead layer within the ferromagnetic materials. While upper, middle, and lower portions 1008, 1006, and 1004 are shown with distinct interfaces between them, clear boundaries may not exist. As apparent, the atomic percent oxygen in capping layer structure 1002 is not uniform throughout from top to bottom.
If the ex-situ oxidation is thorough, the thoroughly-diffused oxygen in the metallic layer will be strongly bonded to all of the Ta in the Ta lattice due to the formation of Ta—O valence bonds, as in the stable compound Ta2O5. This Ta—O valence bonding increases the thickness of the layer by a factor of about 2½ times (i.e. Ta2O5 layer thickness is 2.5 times thicker than the Ta layer thickness). However, underlying ferromagnetic materials, such as sensing layer structure 206 (i.e. for top-type GMR magnetic sensing devices such as in FIG. 10) or AP pinned layer structure 204 (i.e. for bottom-type GMR magnetic sensing devices) may become partially oxidized and form a magnetically “dead” layer from the diffusion of non-bonded oxygen into it. If capping layer structure 1002 is sufficiently oxidized uniformly from top to bottom without un-bonded Ta or oxygen diffusion into underlying ferromagnetic materials, the sensor properties may be enhanced as mentioned above. Uniform oxidation performed subsequent to metallic layer deposition is practical with metallic layer thicknesses of about 10 Å or less, which is below conventional thickness requirements of between about 20 Å and about 40 Å.
Accordingly, what are needed are SV sensors having capping layer structures which help provide an increased magnetoresistive effect while preserving good soft magnetic properties of the sensing layer. What are also needed are methods in which to sufficiently oxidize metallic materials of a capping layer structure without affecting the underlying sensing layer.
FIG. 11 shows an ABS illustration of a typical multi-layered structure of a tunneling magnetoresistance (TMR) type SV sensor, typically referred to as a magnetic tunnel junction (MTJ) type SV sensor 1100 of the prior art. This read element may be utilized in the slider and disk drive shown and described above in relation to FIGS. 1-8. MTJ type SV sensor 1100 is formed between and in contact with lower (S1) and upper (S2) shield layers 1172 and 1174, which serve as electrically conductive leads (L1 and L2) for the sensor.
MTJ type SV sensor 1100 includes, from bottom to top, a seed (SL) layer 1120, an antiferromagnetic (AFM) pinning layer 1114, an AP pinned layer structure 1104, an insulating tunnel barrier (B11) layer structure 1132, a sensing (F) layer structure 1124, and a capping (C) layer structure 1102. Sensing layer structure 1124 is formed underneath capping layer structure 1102 and over and adjacent insulating tunnel barrier layer structure 1132. AP pinned layer structure 1104 is formed beneath insulating tunnel barrier layer structure 1132 and over and adjacent AFM pinning layer 1114. AFM pinning layer 1114 is formed beneath pinned layer structure 1104 and over and adjacent to seed layer structure 1120. Seed layer structure 1120 is formed over lower shield layer 1172 and underneath AFM pinning layer 1114 for promoting an improved texture of the layers deposited thereon.
The following materials are examples of materials which may be utilized in multilayered MTJ type SV sensor 1100. The first and second shields 1172 and 1174 may be made of any electrically conducting material such as NiFe; seed layer 1120 may be made of any suitable material such as NiFeCr, NiFe, Ta, or Ru; AFM layer 1114 may be made of any suitable material such as PtMn, IrMn or iridium-manganese-chromium (IrMnCr); AP pinned layers 1110 and 1112 may be made of Co or CoFe; APC layer 1108 may be made of Ru; tunnel barrier layer structure 1132 is a made of TaOx, AlOx, MgOx, and TiOx, where x indicates varying oxygen content throughout the thickness of the barrier layer and deviating stoichiometric composition; sensing layer structure 1124 may be made of CoFe and NiFe; and capping layer structure 1102 may be made of Ta. Thicknesses of particular materials may be 200 Å for first and second shield layers; 30 Å of NiFeCr for seed layer 1120; 150 Å of PtMn for AFM layer 1114, 30 Å of CoFe for first AP pinned layer 1110; 8 Å of Ru for APC layer 1108; 30 Å of CoFe for second AP pinned layer 1112; 10 Å TaOx, for tunnel barrier layer structure 1132; 15 Å of CoFe and 15 Å of NiFe for sensing layer structure 1124; and 40 Å of Ta for capping layer structure 1102.
Conventional methods of making tunnel barrier layer structure 1132 of FIG. 11 involve the steps of depositing a metallic layer and subsequently in-situ oxidizing that metallic layer from the top down. The depth of oxygen (O) diffusion into the metallic layer is difficult to precisely control and the oxidation must be performed gently in order not to damage underlying ferromagnetic materials. Furthermore, the form in which the diffused oxygen is found (if at all) throughout such a layer is of importance to sensor performance.
The oxygen may diffuse only to a certain depth into the metallic layer since the oxidation is from the top. Only an upper portion (B113) 1138 of the metallic layer may be sufficiently oxidized from the natural oxidation. In upper portion 1138, the diffused oxygen may be strongly bonded to the Ta in the Ta lattice due to the formation of Ta—O valence bonds, as in the stable compound tantalum oxide (Ta2O5). This Ta—O valence bonding increases the thickness of upper portion 1138 of the layer by a factor of about 2½ times which may limit oxygen diffusion to the remaining portions of the layer. In a middle portion (B112) 1136 of the metallic layer, the diffused oxygen may be loosely bonded in a lower concentration than that found in upper portion 1138, probably in interstitial sites of the Ta lattice. This loosely bonded oxygen also increases the thickness of middle portion 1136 by a varying factor depending on the diffused oxygen concentration. In a lower portion (B111) 1134 of the metallic layer, diffused oxygen may not be found in any appreciable concentration (i.e., lower portion 1134 may be substantially pure Ta), therefore creating a magnetically dead layer. While upper, middle, and lower portions 1138, 1136, and 1134 are shown with distinct interfaces between them, clear boundaries may not exist. As apparent, the atomic percent oxygen in tunnel barrier layer structure 1132 is not uniform throughout from top to bottom.
If the in-situ oxidation is thorough, the thoroughly-diffused oxygen in the metallic layer will be strongly bonded to all of the Ta in the Ta lattice due to the formation of Ta—O valence bonds, as in the stable compound Ta2O5. This Ta—O valence bonding increases the thickness of the layer by a factor of about 2½ times. However, underlying ferromagnetic materials, such as second pinned layer 1112 (i.e. for bottom-type TMR sensing devices such as in FIG. 11) or sensing layer structures (i.e. for top-type TMR sensing devices), may suffer microstructural changes, as in the formation of a magnetically dead layer from the diffusion of non-bonded excess oxygen into it. If tunnel barrier layer structure 1132 is sufficiently oxidized uniformly from top to bottom without un-bonded Ta or oxygen diffusion into underlying ferromagnetic materials, the sensor properties may be enhanced as mentioned above. This gentle sufficient uniform oxidation is practical with metallic layer thicknesses of about 5 Å or less, which is below conventional metallic layer thicknesses of between about 6 Å and about 10 Å.
Accordingly, what are needed are sensors which overcome the deficiencies of the prior art, as well as methods of making the same.